1. Field of the Invention
The present invention relates to a shield developed to eliminate electromagnetic waves interference while testing radio frequency (RF) based products, specifically bit error rate (BER) failures on Bluetooth devices and gain measurement error on wireless local area network (WLAN) products caused by nearby WLAN access points and other transceivers.
2. Introduction
One of the last steps in the manufacturing process of a semiconductor device or an integrated circuit is the quality assurance (QA) process. In the QA process, automatic test equipment (ATE) is used to automatically test the device (device under test or DUT). During this QA process, the ATE applies test signals to the DUT and checks for appropriate responses. Based on the DUT's responses, the ATE marks the DUT as pass or fail by comparing the responses to predetermined signal response patterns. The appropriate response patterns are determined by the type of test employed and the type of product being tested.
DUTs that fail the initial QA process are typically fed through the ATE again to minimize false rejections. Once the DUT fails the second time, it is usually scrapped which will negatively affect production efficiency, cost, and profits. However, not all DUTs scrapped are bad. Variability factors in the test method, equipment, and environment plays an essential role in testing accuracy of the DUT. Minimizing these variability factors will lead to better testing process and higher production yield. The present invention focuses on the minimization of the variability in the test environment.
Device under test (DUT) are often sensitive to electromagnetic interference, particularly at high frequencies. Proper shielding of a DUT is therefore essential because of potential interference and the effect on the test's accuracy. In an un-shielded and high interference environment, many DUTs could be falsely rejected because of measurement errors that can be attributed to electromagnetic interference. Reducing this type of interference can be done in two ways. The first way is to eliminate the source of the interference. The second is to shield the DUT.
Surprisingly, it can be very difficult to eliminate the source of the high frequency that causes the interference. High frequency devices are abundant. Often time these devices are located in the same environment with the DUT such as switched mode power supplies, computer clocks, laptops, mobile phones, and nearby WLAN access points.
Shielding is the second way to reduce electromagnetic interferences. One option is to shield the test room or the test area in which the DUT are being tested; however, this is a prohibitively expensive solution. The other option is to shield the ATE system. This option is also not viable, because ATE system is typically very large.
Generally, a compact shielding solution can be developed for an ATE. But there are few, if any, shielding solutions available on the market. Test equipment and socket vendors want to customize and integrate a shielding into their socket base but are not doing so due to high cost which in turn makes the test equipment not very marketable. Moreover, any of these solutions would be specific to that manufacturer and that socket footprint, which is not scalable.
Accordingly, what is needed is a low cost testing device that is capable of significantly attenuating interfering signals to a level below the sensitivity of the device under test (DUT).